I suggest that you change your title, and/or the way your post is presented. It is quite confusing on first read (since people would just skim through your post).
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nhahtdhMar 13 '13 at 7:51

4

The same thing is true for is:bacon, isaccepted:possibly, and closed:unjustly, i.e. any invalid search operator.
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balpha♦Mar 13 '13 at 8:11

1

Well I also think this is a bug, the engine should return 0 results for invalid search terms. I wasted some time looking for what I searched in totally irrelevant results before I figured out what was going on...
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spykJun 13 at 13:30

The user has an account on another SE site and the post was migrated to a site where they don't have an account

The user requested deletion of their account (generally this shows a greyed out userXYZ, but this seems to be a special case)

Also, User seaching the Data Explorer will give you a list of users who have an account on data.SE. You have to write a SQL query (Select * from users where DisplayName='Gnome') and run it (though in this case the account probably was deleted a long time ago and won't be on data.SE).

I think you've missed the thrust of the question: Danny is asking why this query causes the search engine to return every single question and every single answer from the database. "Who's Gnome?" is just a side question.
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EnergyNumbersMar 13 '13 at 7:16

The post is not migrated, so the user is probably deleted.
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Toon KrijtheMar 13 '13 at 7:18

@ToonKrijthe: Yep, though generally deleted users are have their usernames replaced with userXYZ
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ManishearthMar 13 '13 at 7:27